Learn English – Left and Right are “Sides”; Front and Rear are “Ends”; Top and Bottom are…

I'm looking for a fitting word in the context of design/engineering. We have long structural members that go in an assembly and we need to be able to describe them based on their orientation and location.

EDIT: I'm looking for a word that makes sense in the following context:

EDIT (CONT'D): Someone putting this thing together in the real world should be able to pick up a flange labeled "[word for top-and-bottom] flange" and confidently put it in the right place.

We have an appropriate word for each orientation:

• Members oriented front-to-rear: Longitudinal members
• Members oriented left-to-right: Lateral members
• Members oriented top-to-bottom: Vertical members

However, I'm stumped for one of the words when it comes to location:

• Members located on the front or rear: End members
• Members located on the left or right: Side members
• Members located on the top or bottom: ??? members

Let me give a few usage examples. These are some examples of how we might name members in an assembly:

• Vertical Side Flange (a vertical flange located on the sides)
• Vertical End Flange (a vertical flange located on the ends)
• Lateral End Flange (a lateral flange located on the ends)
• Lateral ??? Flange (a lateral flange located on the top and bottom)
• Longitudinal Side Flange (a longitudinal flange located on the sides)
• Longitudinal ??? Flange (a longitudinal flange located on the top and bottom)

Another way to describe the positions is using the "plural" sense:

• The longitudinal extremes are the "Ends"
• The lateral extremes are the "Sides"
• The vertical extremes are the… ???

As a usage example, we also might put a note to the following effect on a drawing:

• "Repeat on both sides"
• "Repeat on both ends"
• "Repeat on both …???"

Ideally, I'm looking for a word that can work in both singular plural and contexts, like "end/ends" and "side/sides" do.

We have such fitting words for the left-to-right and front-to-back extremes of something… I find it hard to believe that the English language has no fitting word for the vertical extremes of something. If it really doesn't, I would be strongly in favor of making up one…